A lithium secondary battery has a reduced weight and high energy density, and has been expected to be used as a drive power supply for hybrid cars, electric vehicles, and the like in addition to a power supply for portable small electronic devices. Lithium metal was initially used as the negative electrode material for the lithium secondary battery. However, since lithium ions deposit and grow on the negative electrode in the form of dendrites during charge, and decrease the capacity upon falling, or cause a short circuit, a graphite material that does not form such dendrites has been proposed.
A graphite material exhibits a high charge-discharge efficiency due to an excellent lithium ion dope-undope capability (extraction-insertion capability). Moreover, since the potential of the graphite material during charge and discharge is almost equal to that of lithium metal, it is possible to obtain a high-voltage battery, for example.
A known method for producing a graphite powder (graphite material) for use as a lithium secondary battery negative electrode material includes mixing 60 parts by mass of synthetic pitch tar (binder) with 100 parts by mass of green pitch coke, forming the mixture in the shape of a block at a cold isostatic pressure of 900 kgf/cm2, heating the resulting block at 1000° C. and 2800° C. to effect graphitization, and grinding and classifying the resulting graphitized block (see Example 3 of Patent Document 1 (JP-A-2008-059903)).